HIDDEN PROCESSES 155 



in many animals, more especially in birds in 

 the growth of epidermic appendages, such as 

 the wattles of the male turkey, or the horns of 

 the stag. In man also, when puberty is reached , 

 there are changes in the general nutrition of 

 the female and in the appearance of the beard 

 in the male. Such phenomena have been 

 termed those of complemental nutrition, a 

 term of little meaning unless we associate with 

 it the conception that the nutrition of such 

 organs in some way affects the quality of the 

 blood, possibly by an internal secretion, and 

 that this altered quality affects the nutrition 

 of other organs. 



86 We have now to approach what is 

 known regarding the processes in the living 

 cell on which the ultimate phenomena of 

 nutrition depend. Each cell, as we have seen, 

 is bathed by lymph which has been furnished 

 by the blood. Under no circumstances does 

 the blood come into direct contact with the 

 living tissues outside the vessels. No doubt 

 the walls of the vessels themselves contain 

 living elements, and we may regard the wall 

 of an ultimate capillary as alive. But, so far 



